A switching assembly is a type of device that interrupts the flow of current. Some switching assemblies are used in systems that interrupt the flow of electricity in a high voltage electrical circuit. FIG. 1A shows a perspective view of a conventional switching assembly 100. FIG. 1B shows a perspective cross-sectional view of the conventional switching assembly 100 of FIG. 1A. Referring to FIGS. 1A and 1B, the conventional switching assembly 100 includes a single-piece bushing 110, an upper terminal 120, a fixed lower terminal 130, and a switching medium 140.
The single-piece bushing 110 is integrally formed and includes a first end 111, a second end 112, a sidewall 113 extending from substantially the perimeter of the first end 111 to substantially the perimeter of the second end 112, and a cavity 109 extending from the first end 111 to the second end 112 within the single-piece bushing 110. The sidewall 113 includes a first portion 114 and a second portion 115. The first portion 114 is substantially conical-shaped and extends from the first end 111 towards the second end 112 and integrally transitions into the second portion 115. The second portion 115 is substantially cylindrical-shaped and extends from the second end 112 towards the first end 111 and integrally transitions into the first portion 114. According to FIGS. 1A and 1B, the first end 111 has a smaller circumference than the second end 112.
The single-piece bushing 110 also includes an upper terminal opening 116, a fixed lower terminal opening 117, a flange 118, and a plurality of weathersheds 119. The upper terminal opening 116 is formed at the first end 111 and is dimensioned to receive the upper terminal 120. The fixed lower terminal opening 117 is formed along the first portion 115 and is dimensioned to receive the fixed lower terminal 130. The flange 118 is formed at the second end 112 and is coupleable to a tank (not shown) in a sealed manner. A seal (not shown) is insertable into the underside area of the flange 118, which thereby allows the flange 118 to be sealably coupled to the tank. The weathersheds 119 are integrally formed along the sidewall 113 and extend radially outward from the sidewall 113. A portion of the weathersheds 119 is located along the first portion 114 of the sidewall 113 above the fixed lower terminal opening 117, while another portion of the weathersheds 119 is located along the second portion 115 of the sidewall 113. The design of the single-piece bushing 110 can be redesigned depending upon the system design requirements. For example, the length of the single-piece bushing 110 can be made longer or shorter. Also, the number and diameters of the weathersheds 119, along the first portion 114 and/or along the second portion 115, can be increased or decreased. Further, the shape of the sidewall 113 can be different. However, any changes to the design of the single-piece bushing 110 will need a change in the design of the tool (not shown) used to fabricate the single-piece bushing 110, thereby increasing fabrication costs.
The upper terminal 120 is fabricated using an electrically conductive material and is inserted at least partially within the upper terminal opening 116. The upper terminal 120 includes threads (not shown) which couple to mating threads (not shown) positioned within the upper terminal opening 116. Once coupled to the single-piece bushing 110, the exposed portion of the upper terminal 120 provides a connection point to an electrical source (not shown), thereby allowing current to enter into the conventional switching assembly 100. The shape and materials used to fabricate the upper terminal 120 are known to people having ordinary skill in the art.
The fixed lower terminal 130 is fabricated using an electrically conductive material and is inserted at least partially within the fixed lower terminal opening 117. The fixed lower terminal 130 includes threads (not shown) which couple to mating threads (not shown) positioned within the fixed lower terminal opening 117. The fixed lower terminal 130 is located in a fixed manner with respect to the single-piece bushing 110. Once coupled to the single-piece bushing 110, the exposed portion of the fixed lower terminal 130 provides a connection point to a load (not shown), thereby allowing current to exit the conventional switching assembly 100. The shape and materials used to fabricate the fixed lower terminal 130 is known to people having ordinary skill in the art. Although the upper terminal 120 is electrically coupled to the electrical source and the fixed lower terminal 130 is electrically coupled to the load, the upper terminal 120 is electrically coupled to the load and the fixed lower terminal 130 is electrically coupled to the electrical source in other examples.
The switching medium 140 is located within the cavity 109 and is electrically coupled to both the upper terminal 120 and the fixed lower terminal 130. The switching medium 140 is electrically coupled to the fixed lower terminal 130 using an electrical pathway 150, which also is located within the cavity 109. The electrical pathway 150 can be a flexible copper wire. When in the closed condition, the switching medium 140 allows electrical current to flow from the upper terminal 120 to the fixed lower terminal 130. When in the open condition, however, the switching medium 140 prevents electrical current to flow from the upper terminal 120 to the fixed lower terminal 130. Although not described in detail, other components can be inserted into the cavity 109. For example, a buffer material (not shown), such as polyurethane foam, urethane, or silicone, is insertable within a portion of the cavity 109 which extends from about the upper portion of the switching medium 140 to about the uppermost portion of the cavity 109. The buffer material is usable in many types of switching mediums 140, such as a vacuum bottle type, to improve the resistance of electrical discharge across the device and act as a thermal expansion buffer. Although not shown, a control device is interfaced with the switching medium 140 through a series of electromechanical interconnections, which determines when the switching medium 140 is to operate and interrupt the flow of current. This control device can be located within the cavity 109 or outside the cavity 109 depending upon the design choices.
The conventional switching assembly 100 is often difficult to install in service due to the fixed location of the fixed lower terminal 130. The fixed lower terminal 130 should be accessible, but oftentimes is not, for electrically coupling the load thereto. The installation of the conventional switching assembly 100 in service requires extensive engineering and planning, and may involve some degree of disassembly of the conventional switching assembly 100 from the tank. For example, in situations where the fixed lower terminal 130 is not accessible, the flange 118 of the conventional switching assembly 100 is disassembled from the tank, the conventional switching assembly 100 is rotated so that the location of the fixed lower terminal 130 is accessible, and the conventional switching assembly 100 is reassembled to the tank. During this reassembly, the seal between the flange 118 and the tank can be compromised, thereby allowing a path for moisture and environmental contamination to enter the conventional switching assembly 100.